To address hypertension, heart failure and their associated cardiovascular and nervous system disorders, the present invention provides a number of devices, systems and methods by which the blood pressure, nervous system activity, and neurohormonal activity may be selectively and controllably regulated by activating baroreceptors. By selectively and controllably activating baroreceptors, the present invention reduces excessive blood pressure, sympathetic nervous system activation and neurohormonal activation, thereby minimizing their deleterious effects on the heart, vasculature and other organs and tissues.
The present invention provides systems and methods for treating a patient by inducing a baroreceptor signal to effect a change in the baroreflex system (e.g., reduced heart rate, reduced blood pressure, etc.). The baroreceptor signal is activated or otherwise modified by selectively activating baroreceptors. To accomplish this, the system and method of the present invention utilize a baroreceptor activation device positioned near a baroreceptor in the carotid sinus, aortic arch, heart, common carotid arteries, subclavian arteries, and/or brachiocephalic artery. Preferably, the baroreceptor activation device is located in the right and/or left carotid sinus (near the bifurcation of the common carotid artery) and/or the aortic arch. By way of example, not limitation, the present invention is described with reference to the carotid sinus location.
Generally speaking, the baroreceptor activation device may be activated, deactivated or otherwise modulated to activate one or more baroreceptors and induce a baroreceptor signal or a change in the baroreceptor signal to thereby effect a change in the baroreflex system. The baroreceptor activation device may be activated, deactivated, or otherwise modulated continuously, periodically, or episodically. The baroreceptor activation device may comprise a wide variety of devices which utilize electrodes to directly or indirectly activate the baroreceptor. The baroreceptor may be activated directly, or activated indirectly via the adjacent vascular tissue. The baroreceptor activation device will be positioned outside the vascular wall. To maximize therapeutic efficacy, mapping methods may be employed to precisely locate or position the baroreceptor activation device.
The present invention is directed particularly at electrical means and methods to activate baroreceptors, and various electrode designs are provided. The electrode designs may be particularly suitable for connection to the carotid arteries at or near the carotid sinus, and may be designed to minimize extraneous tissue stimulation. While being particularly suitable for use on the carotid arteries at or near the carotid sinus, the electrode structures and assemblies of the present invention will also find use for external placement and securement of electrodes about other arteries, and in some cases veins, having baroreceptor and other electrically activated receptors therein.
In a first aspect of the present invention, a baroreceptor activation device or other electrode useful for a carotid sinus or other blood vessel comprises a base having one or more electrodes connected to the base. The base has a length sufficient to extend around at least a substantial portion of the circumference of a blood vessel, usually an artery, more usually a carotid artery at or near the carotid sinus. By “substantial portion,” it is meant that the base will extend over at least 25% of the vessel circumference, usually at least 50%, more usually at least 66%, and often at least 75% or over the entire circumference. Usually, the base is sufficiently elastic to conform to said circumference or portion thereof when placed therearound. The electrode connected to the base is oriented at least partly in the circumferential direction and is sufficiently stretchable to both conform to the shape of the carotid sinus when the base is conformed thereover and accommodate changes in the shape and size of the sinus as they vary over time with heart pulse and other factors, including body movement which causes the blood vessel circumference to change.
Usually, at least two electrodes will be positioned circumferentially and adjacent to each other on the base. The electrode(s) may extend over the entire length of the base, but in some cases will extend over less than 75% of the circumferential length of the base, often being less than 50% of the circumferential length, and sometimes less than 25% of the circumferential length. Thus, the electrode structures may cover from a small portion up to the entire circumferential length of the carotid artery or other blood vessel. Usually, the circumferential length of the elongate electrodes will cover at least 10% of the circumference of the blood vessel, typically being at least 25%, often at least 50%, 75%, or the entire length. The base will usually have first and second ends, wherein the ends are adapted to be joined, and will have sufficient structural integrity to grasp the carotid sinus.
In a further aspect of the present invention, an extravascular electrode assembly comprises an elastic base and a stretchable electrode. The elastic base is adapted to be conformably attached over the outside of a target blood vessel, such as a carotid artery at or near the carotid sinus, and the stretchable electrode is secured over the elastic base and capable of expanding and contracting together with the base. In this way, the electrode assembly is conformable to the exterior of the carotid sinus or other blood vessel. Preferably, the elastic base is planar, typically comprising an elastomeric sheet. While the sheet may be reinforced, the reinforcement will be arranged so that the sheet remains elastic and stretchable, at least in the circumferential direction, so that the base and electrode assembly may be placed and conformed over the exterior of the blood vessel. Suitable elastomeric sheets may be composed of silicone, latex, and the like.
To assist in mounting the extravascular electrode over the carotid sinus or other blood vessel, the assembly will usually include two or more attachment tabs extending from the elastomeric sheet at locations which allow the tabs to overlap the elastic base and/or be directly attached to the blood vessel wall when the base is wrapped around or otherwise secured over a blood vessel. In this way, the tabs may be fastened to secure the backing over the blood vessel.
Preferred stretchable electrodes comprise elongated coils, where the coils may stretch and shorten in a spring-like manner. In particularly preferred embodiments, the elongated coils will be flattened over at least a portion of their lengths, where the flattened portion is oriented in parallel to the elastic base. The flattened coil provides improved electrical contact when placed against the exterior of the carotid sinus or other blood vessel.
In a further aspect of the present invention, an extravascular electrode assembly comprises a base and an electrode structure. The base is adapted to be attached over the outside of a carotid artery or other blood vessel and has an electrode-carrying surface formed over at least a portion thereof. A plurality of attachment tabs extend away from the electrode-carrying surface, where the tabs are arranged to permit selective ones thereof to be wrapped around a blood vessel while others of the tabs may be selectively removed. The electrode structure on or over the electrode-carrying surface.
In preferred embodiments, the base includes at least one tab which extends longitudinally from the electrode-carrying surface and at least two tabs which extend away from the surface at opposite, transverse angles. In an even more preferred embodiment, the electrode-carrying surface is rectangular, and at least two longitudinally extending tabs extend from adjacent corners of the rectangular surface. The two transversely angled tabs extend at a transverse angle away from the same two corners.
As with prior embodiments, the electrode structure preferably includes one or more stretchable electrodes secured to the electrode-carrying surface. The stretchable electrodes are preferably elongated coils, more preferably being “flattened coils” to enhance electrical contact with the blood vessel to be treated. The base is preferably an elastic base, more preferably being formed from an elastomeric sheet. The phrase “flattened coil,” as used herein, refers to an elongate electrode structure including a plurality of successive turns where the cross-sectional profile is non-circular and which includes at least one generally flat or minimally curved face. Such coils may be formed by physically deforming (flattening) a circular coil, e.g., as shown in FIG. 24 described below. Usually, the flattened coils will have a cross-section that has a width in the plane of the electrode assembly greater than its height normal to the electrode assembly plane. Alternatively, the coils may be initially fabricated in the desired geometry having one generally flat (or minimally curved) face for contacting tissue. Fully flattened coils, e.g., those having planar serpentine configurations, may also find use, but usually it will be preferred to retain at least some thickness in the direction normal to the flat or minimally curved tissue-contacting surface. Such thickness helps the coiled electrode protrude from the base and provide improved tissue contact over the entire flattened surface.
In a still further aspect of the present invention, a method for wrapping an electrode assembly over a blood vessel comprises providing an electrode assembly having an elastic base and one or more stretchable electrodes. The base is conformed over an exterior of the blood vessel, such as a carotid artery, and at least a portion of an electrode is stretched along with the base. Ends of the elastic base are secured together to hold the electrode assembly in place, typically with both the elastic backing and stretchable electrode remaining under at least slight tension to promote conformance to the vessel exterior. The electrode assembly will be located over a target site in the blood vessel, typically a target site having an electrically activated receptor. Advantageously, the electrode structures of the present invention when wrapped under tension will flex and stretch with expansions and contractions of the blood vessel. A presently preferred target site is a baroreceptor, particularly baroreceptors in or near the carotid sinus.
In a still further aspect of the present invention, a method for wrapping an electrode assembly over a blood vessel comprises providing an electrode assembly including a base having an electrode-carrying surface and an electrode structure on the electrode-carrying surface. The base is wrapped over a blood vessel, and some but not all of a plurality of attachment tags on the base are secured over the blood vessel. Usually, the tabs which are not used to secure an electrode assembly will be removed, typically by cutting. Preferred target sites are electrically activated receptors, usually baroreceptors, more usually baroreceptors on the carotid sinus. The use of such electrode assemblies having multiple attachment tabs is particularly beneficial when securing the electrode assembly on a carotid artery near the carotid sinus. By using particular tabs, as described in more detail below, the active electrode area can be positioned at any of a variety of locations on the common, internal, and/or external carotid arteries.
In another aspect, the present invention comprises pressure measuring assemblies including an elastic base adapted to be mounted on the outer wall of a blood vessel under circumferential tension. A strain measurement sensor is positioned on the base to measure strain resulting from circumferential expansion of the vessel due to a blood pressure increase. Usually, the base will wrap about the entire circumference of the vessel, although only a portion of the base need be elastic. Alternatively, a smaller base may be stapled, glued, clipped or otherwise secured over a “patch” of the vessel wall to detect strain variations over the underlying surface. Exemplary sensors include strain gauges and micro machined sensors (MEMS).
In yet another aspect, electrode assemblies according to the present invention comprise a base and at least three parallel elongate electrode structures secured over a surface of the base. The base is attachable to an outside surface of a blood vessel, such as a carotid artery, particularly a carotid artery near the carotid sinus, and has a length sufficient to extend around at least a substantial portion of the circumference of the blood vessel, typically extending around at least 25% of the circumference, usually extending around at least 50% of the circumference, preferably extending at least 66% of the circumference, and often extending around at least 75% of or the entire circumference of the blood vessel. As with prior embodiments, the base will preferably be elastic and composed of any of the materials set forth previously.
The at least three parallel elongate electrode structures will preferably be aligned in the circumferential direction of the base, i.e., the axis or direction of the base which will be aligned circumferentially over the blood vessel when the base is mounted on the blood vessel. The electrode structures will preferably be stretchable, typically being elongate coils, often being flattened elongate coils, as also described previously.
At least an outer pair of the electrode structures will be electrically isolated from an inner electrode structure, and the outer electrode structures will preferably be arranged in a U-pattern in order to surround the inner electrode structure. In this way, the outer pair of electrodes can be connected using a single conductor taken from the base, and the outer electrode structures and inner electrode structure may be connected to separate poles on a power supply in order to operate in the “pseudo” tripolar mode described herein below.
To address low blood pressure and other conditions requiring blood pressure augmentation, the present invention provides electrode designs and methods utilizing such electrodes by which the blood pressure may be selectively and controllably regulated by inhibiting or dampening baroreceptor signals. By selectively and controllably inhibiting or dampening baroreceptor signals, the present invention reduces conditions associated with low blood pressure.